RF power amplifiers are known in the art for use in amplifying RF signals for broadcasting purposes, including radio and television. These amplifiers may be employed for broadcasting either analog television signals, known as the NTSC format, or digital signals, known as the ATSC format.
In the amplification of such RF signals, it is common to split the RF signal to be amplified into portions and then amplify each portion and combine the amplified portions to provide an amplified RF signal for application to an antenna system.
The known methods of splitting and combining the RF signals take place at both a module level and a group (of modules) level. That is, a plurality of power amplifier modules may be grouped together and housed in a common power amplifier cabinet. The group (or cabinet) may receive an RF signal which is then split into portions and each portion is fed to one power amplifier module for amplification. The amplified RF signals from the modules are combined.
Such an amplifier system may have several such groups of power amplifier modules housed in several different power amplifier cabinets. An RF signal which is received by the system is split into portions with each portion being fed to the group of power amplifiers housed within one of the power amplifier cabinets. Again, within each group the RF signal is split into portions with each portion being supplied through one of the groups of power amplifier modules for amplification. The outputs from the various groups are then combined and fed to an antenna system.
As an example, the system as described above may include one to five power amplifier groups (or cabinets) with each group containing 16 power amplifier modules and each module containing 12 power amplifiers. The RF output signals from each module may be on the order of 400 watts. Consequently, each cabinet may provide an RF output on the order of 5,000 watts and a system of five cabinets may provide an RF output on the order of 25,000 watts.
Transmitters that employ RF power amplifiers as described above are frequently expected to be constantly operating or continuously "on the air" even though equipment failures take place. Some equipment failures are of a type referred to as a "single point failure". Such a failure in some prior art transmitter systems has resulted in transmitter shut-down. For example, in a transmitter employing an IOT (inductive output tube) the amplification takes place in a single vacuum tube. If the tube fails, the transmitter is shut down and, hence, is "off the air".
It is desirable that equipment failures do not result in a transmitter shutting down and being "off the air". To this end, it is desired to provide a system exhibiting a great amount of redundancy of equipment and functional control so that there is a backup or a work-around for each potential single point failure situation in order to keep the transmitter "on the air". It is also desirable to provide "on air" serviceability of components. Many of such components may be "hot pluggable" in the sense that they may be removed and replaced without shutting off the power.
It is also desirable that the controls for the power amplifier system include two control systems which work in parallel and wherein each is capable of operating the power amplifier system with one control system serving as the normal or main control system and the other control system serving as a back up or life support control system.